Viewing Mars

In Fall 2003, Mars comes very close to the Earth, providing an
opportunity for detailed observations.

Background Reading:Stars & Planets,
p. 347 to 355 (Mars)

This table provides simulated images and other data for Mars as it
will appear at 21:30 (9:30 pm) on each Tuesday through the end of
October. Each date links to an image showing how Mars will appear on
that evening. The diameter column gives the angular diameter,
measured in seconds of arc, of the planet itself. The altitude column
gives the angle in degrees between Mars and the horizon as seen from
Honolulu; large altitudes provide the best views. The longitude
column indicates what part of Mars will be facing the Earth, and the
final column lists surface features which should be visible.

As this table shows, there is a trade-off between altitude and
diameter. Mars is closest to the Earth at the end of August, and if
other things were equal, we would expect the best views then. But on
that date, Mars will still be quite low in the sky at 21:30; we would
need to wait until midnight to take full advantage of Mars's
proximity. From late August through mid September, the altitude Mars
attains at 21:30 increases dramatically, while the planet's apparent
diameter decreases only slightly. Thus the best views will probably
be in early to mid September, when the planet is significantly higher
in the sky but only slightly more distant than in late August.

Another factor to consider is the longitude, which determines which
side of Mars is turned toward the Earth. Mars rotates on its axis
once every 24 hours and 37 minutes, so in one week it makes
6.82 rotations. Thus, if we observe Mars every week at the same time,
we will see a somewhat different part of Mars each week; the surface
features which are facing directly toward the Earth one week will
appear toward the edge of the planet's disk the next week. For
example, Syrtis Major, the planet's most prominent feature, will
appear on the east side of Mars on 09/09/03,
and on the west side on 09/16/03.
By observing Mars every week for five weeks or more, we will get a
chance to see every part of the Martian globe (except for
Mars's north pole, which is currently tipped away from the Earth).

A final factor is the weather, both here and on Mars itself. Dust
storms occasionally occur on Mars; in extreme cases, they can obscure
the entire surface of the planet for weeks on end! According to some
experts, dust storms are more likely during summer in Mars's southern
hemisphere, which begins in September 2003. To have the best chance
of seeing Mars despite the real possibility of dust storms, we will
observe the planet whenever possible.

WEB RESOURCES

Animation showing Mars as seen from the Earth each night from
08/26/03 to 12/30/03 at 21:00 (08/27/03, 07:00 UT
to 12/31/03, 07:00 UT). This animation shows one
frame per day, so Mars completes slightly less than one
revolution between frames and thus appears to rotate
backwards. Generated using NASA's Solar System
Simulator.

Animation showing Mars as seen from the Earth from 09/16/03,
20:00 to 09/17/03, 00:00 (09/17/03, 06:00 to 10:00
UT). The long version shows local time in the
upper right. Generated using NASA's Solar System
Simulator.